1. Field of the Invention
This invention relates generally to surveying apparatus and earth-grading machinery, and relates more particularly to three-dimensional position sensing apparatus and methods that utilize laser reference stations and one or more portable position sensors.
2. Description of the Relevant Art
According to conventional practice, the process of transforming a tract of land into a graded surface involves several tasks, typically beginning with the task of surveying the land in order to create a contour map or other graphical representation of the pre-existing state of the land. Surveying involves the delineation of the form, extent, and position of the tract of land based on linear and angular measurements of the land. According to conventional practice, surveying is at least a two person job, with one person operating a measuring instrument from a generally stationary position and the other person transporting and positioning a grade rod or other reference to be sighted by the measuring instrument. The measuring instrument, such as a transit, theodolite, distance meter, or total station, is positioned at a known distance and angle from a reference, or bench mark, position. The grade rod is sequentially positioned at one or more locations, and at each such location, the distance and angle of the grade rod with respect to the position of the measuring instrument is determined and recorded. Distances may be measured manually with a steel tape or chain, or may be measured optically by the measuring instrument utilizing various means such as a retroreflector on the grade rod. Angles are typically measured in both horizontal and vertical planes, with an azimuth angle defined as the horizontal angle measured clockwise from north, and a zenith angle defined as the vertical angle measured downward from the vertical.
From the distance and angle information obtained in the survey, and through application of the principles of geometry and trigonometry, the surface of the tract of land can be characterized and presented in graphical form. The position or location of any point on the tract of land can be represented in a variety of three-dimensional coordinate systems such as X,Y,Z, or R,.THETA.,Z, where X,Y,Z denotes a Cartesian coordinate system in which the X-Y plane is horizontal and the Z axis is vertical, and where R,.THETA.,Z denotes a cylindrical coordinate system in which the R-.THETA. plane is horizontal and the Z axis is vertical. The X,Y or R,.THETA. coordinates are measured in a horizontal plane with respect to some bench mark position, while the Z coordinate is the elevation measured with respect to some horizontal reference plane, such as mean sea level.
After the tract of land has been surveyed, a site plan can be drawn up to define what the contours and elevations of the land should be after grading. In accordance with conventional practices, the site is then marked with stakes in order to guide the operators of earth-moving equipment while they grade the land into conformity with the site plan. The process of marking involves first defining on the site plan the coordinates of various key locations to be marked, and then placing stakes on the land at those locations. The task of marking the land can utilize the same surveying apparatus described above. The grade rod is roughly positioned near a location to be marked, and its position is determined by the measuring instrument. If the grade rod is not exactly positioned at the location to be marked, the position is noted and the grade rod is repositioned and remeasured until the measuring instrument verifies that the grade rod is positioned at the location to be marked. A stake or other marker is then driven into the ground at that point. Like surveying, the process of marking a tract of land is also a task that requires at least two trained people.
In order to designate the desired elevation at the marked locations, the stakes are typically marked with indications of the depth of fill or cut needed to create the desired graded surface at those locations. Such fill or cut information can be determined according to the elevational differences between the contour map of the existing site and the site plan.
After the tract of land has been marked, earth-moving equipment can be used for grading the site. The operators of the earth-moving equipment are guided by the marker stakes in determining where to cut and where to fill. Care must be exercised to avoid damaging the stakes during the grading operation. The site may need to be re-surveyed during or after completion of the grading to verify the accuracy of the graded surface. With the necessary tasks of surveying, marking, and resurveying, the convention practice of transforming a tract of land into a graded surface is unavoidably labor intensive, even apart from the actual grading operations.